FIG. 1 illustrates a prior art 1 port reflectometer. Typical network analyzer calibrations require several standards to be measured at the measurement plane to determine the systematic error coefficients (shown in FIG. 2). Subsequently the calibration devices are removed and set aside while the network analyzer measures the device of interest. Electronic calibration (ECal) simplifies the calibration process by providing a single connection per analyzer port for calibration. Upon completion of the error correction process the ECal device is removed.
Adamien performs automatic calibration of a vector network analyzer (VNA) using multi-state electronic transfer standards inside the test ports of a VNA, behind the reflectometer and applying the “unknown thru” calibration method. A variant prior art method automatically calibrates a VNA with a electronically switchable open, short load standards places behind the test ports and before the reflectometer. The “unknown thru” method may be used to obtain a full 2-port calibration. Neither method allows the system to be configured to measure insertables and non-insertables without additional calibration standards.
U.S. Pat. No. 6,417,674 expanded the “unknown thru” method for multi-port calibration. An initial calibration at the measurement plane using traditional methods is performed. The internal electronic calibration devices are then measure and corrected using the systematic error coefficients obtained from the initial external calibration (shown in FIG. 3). Thus, automatic calibration of the measurement port is performed using the internal electronic calibration devices. Unfortunately, the transmission error coefficients are obtained by using a full 2 port Short-Open-Load-Thru (SOLT) calibration. Due to operating environment conditions, e.g. temperature, movement, age, cables and interconnects often require periodic calibration to maintain accuracy. This technique is not suited for portable instrumentation.